Definition of: diurnal

(dī·ûr′nəl) adjective
1. Happening everyday; daily; also, performed in a day: a planet's diurnal revolution.
2. Done in or pertaining to the daytime: opposed to nocturnal.
3. Med. Increasing in violence by day, as the symptoms of a disease.
4. Bot. Expanding by day and closing at night, as certain flowers.
5. Lasting only one day; ephemeral. See synonyms under DAILY.
—noun
1. Eccl. A service book containing the offices for prime, tierce, sext, nones, vespers, and compline.
2. A diurnal bird or insect.
3. Obs. A journal; diary.
4. Obs. A daily newspaper. [<L diurnalis <diurnus daily <dies day. Doublet of JOURNAL.]
—di·ur′nal·ly adverb